The publication found videos and images that included Islamic State (Isis) beheadings, violent paedophilic cartoons and propaganda that glorified recent terror attacks in the UK and Egypt – all of which it reported to Facebook's moderators.

Instead of removing the content, however, moderators allowed it to remain, saying it did not breach Facebook's "community standards".

A leading lawyer said much of this behaviour was illegal under English law as once the site had been made aware of prohibited content, it had not taken it down.

Julian Knowles, QC, said: "In my view, many of the images and videos identified by The Times are illegal.

"One video appears to depict a sexual assault on a child. That would undoubtedly breach UK indecency laws. The video showing a beheading is very likely to be a publication that encourages terrorism.

"I would argue that the actions of people employed by Facebook to keep up, or remove, reported posts should be regarded as the actions of Facebook as a corporate entity.

"If someone reports an illegal image to Facebook and a senior moderator signs off on keeping it up, Facebook is at risk of committing a criminal offence because the company might be regarded as assisting or encouraging its publication and distribution."

The Times said it has passed on its findings to the London Metropolitan Police as well as the National Crime Agency.

Facebook: 'We are grateful'

In a response to the findings, Justin Osofsky, Facebook's vice-president of global operations, said: "We are grateful to The Times for bringing this content to our attention.

"We have removed all of these images, which violate our policies and have no place on Facebook.

"We are sorry that this occurred. It is clear that we can do better, and we'll continue to work hard to live up to the high standards people rightly expect of Facebook."